This invention generally relates to safety devices for internal combustion powered implements and more particularly to a safety brake to promptly stop an internal combustion engine in the event that the operator moves from his normal operating position. More specifically, the present invention relates to an improved mechanical linkage which will operate without adjustment over the life of the implement regardless of the wear of the brake lining.
The need for safety devices for implements powered by internal combustion engines has long been recognized in order to reduce the possibility of injury to an operator. Many such safety devices have been provided including devices which are generally referred to as "deadman" controls. Such controls may comprise devices to interrupt the ignition circuit of the internal combustion engine as well as braking devices which operate to quickly stop the internal combustion engine when the deadman control lever is no longer actuated by the operator. Typical examples of equipment in which such controls are used are lawnmowers, garden tillers, snowblowers and the like and which require the operator to depress a lever mounted adjacent the handle of the implement to render the implement operational. In the event that the operator releases his grip on the handle, the deadman lever typically moves away from the handle to a position wherein the internal combustion engine is disabled. The braking device itself, which is operated by the deadman control lever, commonly consists of a pivoted braking lever having a friction surface which contacts a surface of the internal combustion engine flywheel when the deadman control lever is not operated. Furthermore, one or more electrical switches may be provided to selectively disable the ignition circuit of the internal combustion engine when the deadman control is in its unoperated position.
Typical examples of such prior art braking devices are provided in U.S. Pat. Nos. 4,394,893; 4,519,486 and 4,757,885 all of which are assigned to the assignee of the present invention and the disclosures of which are incorporated herein by reference. One of the problems with such prior art safety devices has been that the devices included numerous parts, levers, links and the like. This has resulted in substantial cost for the safety devices and, furthermore, has resulted in a substantial tolerance buildup in the construction of such devices thereby making them more difficult to adjust and assemble. While these prior art devices have generally been satisfactory, it is desired to provide an improved safety device having a minimum of pivot points. It is furthermore desired to provide a device wherein the linkages, at their point of interaction, abut each other without any sliding movement therebetween to prevent wear between contacting surfaces and to ensure proper operation of the device, even after extended use.
Other prior art safety braking devices have been provided wherein only a single braking lever, actuated by the deadman control was provided. While these devices had the advantage of simplicity, a problem with these prior art devices has been that, after extended use of the device and wear of the brake surfaces, the deadman control lever needed adjustment to provide a desired range of movement thereof. It is understandably undesirable for the operator to actuate the deadman control lever through a greater distance when the braking surfaces are worn than when the braking surfaces are new. It is therefore desired to provide a safety device for an internal engine powered implement wherein the range of movement of the deadman control is not dependent upon the wear of the friction brake surfaces.
An additional problem with prior art safety devices has been that adjustment of the devices for a variety of implements was not possible without affecting the operation of the device. Such adjustments of the "control effort" is adjustment of the force needed to move the control lever from the "engine disabled" position. This "control effort" also equals the force available to pull the deadman control back to its normal position. It is therefore desired to provide a safety device for an internal combustion engine powered implement wherein adjustment of the "control effort" of the device may be easily accomplished without affecting the operation of the device so that the safety device may be mounted on various implements.